The invention relates to coating of high temperature components. More particularly, the invention relates to coating gas turbine engine vane clusters.
In the aerospace industry, a well-developed art exists regarding the cooling of components such as gas turbine engine components. Exemplary components are gas turbine engine blades and vanes. Exemplary blades and vanes airfoils are cooled by airflow directed through the airfoil to be discharged from cooling holes in the airfoil surface. Also, there may be cooling holes along the vane shroud or vane or blade platform. The cooling mechanisms may include both direct cooling as the airflow passes through the component and film cooling after the airflow has been discharged from the component but passes downstream close to the component exterior surface.
By way of example, cooled vanes are found in U.S. Pat. Nos. 5,413,458 and 5,344,283 and U.S. Application Publication 20050135923. Vane clustering may have several advantages. The reduced engine part count may ease manufacturing and reduce weight. The reduction in the number of platform and shroud gaps (e.g., a halving with doublets) may have performance advantages. First, intergap leakage may correspondingly be reduced. Second, diversion of cooling air to cool gap seals may also be reduced.
Exemplary cooled vanes are formed by an investment casting of a high temperature alloy (e.g., nickel- or cobalt-based superalloy). The casting may be finish machined (including surface machining and drilling of holes/passageways). The casting may be coated with a thermal and/or erosion-resistant coating.
Exemplary thermal barrier coatings include two-layer thermal barrier coating systems An exemplary system includes an NiCoCrAlY bond coat (e.g., low pressure plasma sprayed (LPPS)) and a yttria-stabilized zirconia (YSZ) barrier coat (e.g., air plasma sprayed (APS) or electron beam physical vapor deposited (EBPVD)). With vane clusters (e.g., doublets), each airfoil may interfere with the line-of-sight application of the coating to the adjacent airfoil(s). This may cause local thinning of the applied coating or even gaps.